Is running a good work out?

I would like to start running, but don't have a lot of time on my hands. Would a 20 minute jog 5 times a week help tone my legs and butt? I'm 5'4" and 93lbs, so I'm not at all looking to lose weight. I'm just looking to gain a little muscle. Is this sufficient or do I need to do more? I've been doing squats daily but I'm not seeing results. I'm really only worried about lifting my butt, so if you have any other work out I could do please let me know.
Is running a good work out?
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